There are many uses for lasers that can benefit society, including a wide range of remote sensing applications. One such use can be to measure distance and variety of methods for measuring distances with lasers are known to exist. Examples of these methods include interferometry, laser Doppler displacement, beam modulation telemetry, and pulse time of light.
Laser interferometers typically provide measurement of displacement from a starting position rather than a measurement of position. The instrument reading is typically set to zero as the initial position of the moving part, and the motion is then measured relative to this zero position. Laser interferometry or distance measurement must be used in a controlled environment. Accordingly this method is typically used in manufacturing applications such as checking the location of work holding fixtures, checking the motion of machining tools, and similar applications.
Laser Doppler displacement distance measurement takes advantage of the Doppler shift of laser frequency effected when a stabilized laser is reflected from a moving surface. This frequency shift can be measured and converted to a measurement of surface displacement, i.e., the difference between a start position and position of an object.
Neither interferometric nor Doppler displacement methods can be used to measure large distances in uncontrolled environments. In particular, fluctuations of the density of the atmosphere over paths exceeding a few hundred feet make these methods impractical.
A common method of distance measurement used outdoors over long distances involves amplitude modulation of a laser beam and projection of the modulated beam toward a target. Distance is measured by comparing the phase of the modulated amplitude of returning light with the phase of the modulated amplitude of emitted light.
Pulse laser range finders are also commonly used to determine large distances. Commercial applications include generation of terrain maps, calibration of aircraft radar, and measurements of ranges of aircraft and ground vehicles. Pulse laser range finders emit a short pulse of laser light and measure the transit time for the pulse to reach a visible target, and for the reflected pulse to return to a receiver located near the laser.
These and other methods for measuring distances are common in the art and they provide many benefits to society. While such devices are well known they do not teach or disclose the device and method that is the subject of the current application and is disclosed below.